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Bleeding hydraulic cylinders

Bleeding hydraulic cylinders

Bleeding hydraulic cylinders

While this may seem very fundamental, how does one bleed a hydraulic cylinder when the rod end port has a welded tube that leads down to its flare connection at the head end. This cylinder lies horizontal when retracted and is tilted rod end up when extended. It always seems to trap some air. I am bleeding by simply loosening the fitting at the end that I am stroking it to to let the air/oil out.

RE: Bleeding hydraulic cylinders

First of all, is the air going to cause a problem if it trapped in the annulus of the cylinder when the cylinder supports the load on the full bore?

Does the cylinder ever go over centre? If it does not then leave the air in and let the oil absorb it.

If you really do need to remove the air, split the fitting at the end of the welded tube and start the cylinder extending. Tighten the fitting before the cylinder stops otherwise when the cylinder relaxes, it will pull air into the tube.

This is not a fundamental problem, removing air from cylinders can be very tricky, the best idea is to stop it getting in in the first place.

Good luck!


RE: Bleeding hydraulic cylinders

when first installing or re installing - pressurise piston
end to full stroke - several times ... avoid accidents

& injuries.

RE: Bleeding hydraulic cylinders

Hmech has good synopsis. Maybe it matters, maybe not.

If load reverses, can be very dangerous expecially at startup. Our shop threw a big conveyor on the ground as the load reversed (past center) and they found out that meter out flow controls and counterbalances only work with liquids, not compressible air!

Loosening the fitting works if JIC flare, but caution if split flange or Oring face seal. The oring can be slightly extruded and leak or blow out later.


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